1. Field of the Invention
The present invention relates to self-propelled, walk-behind power tools, such as lawn mowers, snow blowers or power sweepers, or like equipment. More particularly, the invention involves an effective, yet less expensive, drive system which is able to independently operate each drive wheel of the power deck of such tools in a manner to effect accurate and safe operation thereof.
2. Description of the Related Art
Although the present invention has utility in walk-behind snow blowers, power sweepers, or the like, the most common utilization of the invention is anticipated for lawn mowing equipment of the concerned type, and particularly, in large capacity, commercial walk-behind mowers. Consequently, except where otherwise expressly stated, the description herein is directed to walk-behind lawn mowing equipment, particularly large capacity lawn mowers.
Large capacity commercial-type self-propelled walk-behind lawn mowers commonly have a power deck containing two driven wheels and handle bars mounting the operating handles for the various mower control elements. The mower or tool deck, which connects with the power deck, carries idler or caster wheels to support and balance the mower deck.
Desirably, power input to the drive wheels is effected separately and independently to the respective drive wheels. This allows the machine to be effectively steered by varying the driving input and the braking of one wheel with respect to the other whereby the machine is able to turn about a tight radius.
Most commercial lawn mowers of the prior art employ drive wheels and mower blades which are belt-driven by a motor through transmission systems that utilize output-varying devices for regulating the operation of the various tools and wheel drives. The transmission systems may be hydrostatic transmissions which comprise at least one pump connected to the engine output, typically by a belt and pulley system. The pump or pumps are operable to drive hydraulic motors that are drivingly connected to the respective mower drive wheels and that are independently controlled by means of operating controls mounted on the mower handle bars. Hydrostatic transmissions, although relatively high in cost, have the advantage that the speed and direction of each wheel can be infinitely varied between a lower limit and an upper limit with fewer moving parts than are contained in a conventional gear-operated transmission.
Hydrostatic transmissions have the further advantage that the drive wheels of the power deck can be directly coupled to the hydraulic motor connected to the hydrostatic transmission and, as with hydrostatic transmissions arranged in a lawn mower as shown and described in U.S. Pat. No. 5,127,215 to P. H. Wenzel, the transmission input shaft and the engine drive shaft can rotate about parallel axes whereby the amount of space occupied by the drive train is reduced to an extent that all of the operating parts can be conveniently enclosed by a deck bed which forms a protective covering over the drive train components for safety purposes and to protect the components from damage.
The other, less expensive, form of transmission employed with commercial lawn mowers is a multi-speed geared transmission which obtains input from an engine via a belt and pulley system and outputs, through appropriate gearing, a plurality of discrete speeds to the drive wheels of the power deck. In this form of transmission system, the output from the transmission is typically transmitted to each drive wheel by separate belt and pulley systems. Torque transmitted to the respective wheels is, as shown for example, in U.S. Pat. No. 4,558,558 to H. F. Horner Jr. et al. and U.S. Pat. No. 5,343,678 to T. G. Stuart, controlled by a clutch device in the form of an idler pulley mounted on an arm that pivots into increasing or decreasing engagement with the wheel drive belt so as to vary the tension on the belt and thus the wrap angle about the respective driving and driven pulleys to selectively adjust the torque being transmitted therebetween.
Gear-operated transmissions for self-propelled, commercial-type lawn mowers suffer the disadvantage that idler pulley action to vary torque transmission is conducted under low speed and, accordingly, high torque conditions. Consequently, the drive belts must support this high torque while they are subjected to large tension loads. Thus, the belts are prone to slip relative to the wheel pulley when the drive is subjected to high load conditions. Drive belts of the concerned type are therefore prone to a high degree of wear necessitating frequent replacement.
It is to the amelioration of such problems in self-propelled, walk-behind power tools, such as lawn mowers, to which the present invention is directed.